Contact Current

The picture above is a waveform that was taken from the sink to the floor in a house in Eau Claire, WI. What this can tell you is the amount of ground current present in a home. Whether we are referring to this as ground current, stray voltage, or contact current, know that we are talking about the same thing. Stray voltage is voltage that is not contained in a wire. It runs unchecked through the ground. In a perfect world, there would be no stray voltage and it all would be contained in the wires. In the most extreme cases ground would be used as a last resort. Our ground really would be ground with zero potential. This is not the case because of the increased use of non-linear loads by consumers.

The easiest way to explain this is to relate it to something that is more understandable for most people. In this case it would be driving to and from work every day. You will leave your home and go to work and then come back home. Under normal circumstances, traveling along the roads we have will be the fastest way to get to and from work. However, if there is a traffic jam, then you will more than likely need to take a different route home. If you had off-road capabilities with your vehicle, then cutting across the fields or off-roading might be the fastest route back home. In the end, you are going to end up where you started, which is home. As long as you end up at home it doesn’t matter if you travelled on the roads provided, or made your own roads.

Electricity works in the same way that you go to work. It will go out and come back to where it originally came from (Kirchhoff’s Laws). As long as traveling on the wires is the easiest path, electricity will continue to travel the wires. If this is not the easiest path, electricity will find other paths that are easier to make it back “home”. With the use of more and more non-linear loads, our wires have more things riding on them (examples would be harmonics, transients, and other communications). All of these added things to the power supply make it harder and harder for it to move through wire, especially when the wire is too small. There is a “traffic jam”.

Also, if the wire is too small to allow the electricity to pass through, it can create heat. Enough heat will cause the wire to burn out. In order to stop burn outs, the neutral wires are connected to the ground wires so instead of traveling along the neutral wire, the electricity will flow into the ground and back “home”, essentially “off-roading” through the easiest pathway, the ground. The end result is what we have now, contact current in our homes.

Ground current/stray voltage/ contact current can cause a list of problems for animals and people. During a home inspection we look at the amount of contact current that you have in a house. If your contact current is above 18 µA biological effects relevant to cancer start to take place. That level has been accepted by the NIEHS (National Institute of Environmental Health Sciences). You can read more research on this here. It is important to have this tested to make sure that you are under this limit. Know that based on the demands for power in your area, your contact current will also vary; meaning the more demand there is, the more current that you will have traveling through your home and vice versa. If you are worried about this in your home, you can look at the following things in your house.

One is to look at your plumbing, which is a very common way for ground current to travel into your home. Recall electricity will take the path of least resistance and copper is a great conductor, that is why they use it for electric wire. You can easily test to see if there is current traveling along your pipes by checking to see if the metal pipe is giving off a magnetic field. Anything that has current traveling through it will create a magnetic field. That is a property of physics. A relatively inexpensive item to test this with is a TriField Meter Model 100XE which is easy enough to find. If you have current traveling in your pipes, you will be able to measure a magnetic field there. If you do have a magnetic field, look at replacing 2-3 ft of the copper piping with plastic piping by the main in-take, (this is only for homes that have all copper piping for water). This would go for the sewer lines as well. If you are going to be remodeling or building in the future, look at using materials that are very low conductors, especially in your foam underlayment for flooring. Both of these things are simple things. However, doing all the simple things over time can add up to make a big difference.